Furnace combustion chamber



March 23, 1965 c. F. MEENAN FURNACE COMBUSTION CHAMBER Filed Sept. 19, 1961 United States Patent F 3,174,530 FURNAQE COMBUSTIGN CHAMBER Cyril F. Meenan, 6417 Drake, Lincolnwood, Ill. Filed Sept. 19, 1961, Ser. No. 1355288 4 Claims. (Cl. 158-1) The present invention relates generally to furnaces, and is more particularly directed to an improved means for providing secondary air into the combustion chamber of a furnace which is being fired by a liquid or gaseous fuel.

In the known types of furnaces, and particularly in connection with steam boilers, there is considerable inefiiciency in the combustion chambers, particularly in that combustion of the fuel is incomplete. The incomplete combustion of the fuel, of course, reduces the amount of heat available to the boiler and, also, results in a substantial quantity of organic matter being deposited in the furnace or exhausted to the atmosphere through the chimney. This loss is not only an economical waste, insofar as a substantial percentage of the potential B.t.u. in the fuel is not utilized, but it also presents serious problems with respect to maintenance and with respect to air pollution. In the case of boilers, a substantial deposit of carbon and other organic materials forms in the combustion chamber and are deposited on the tubes, and this must be frequently removed in order to keep the boiler at a reasonably efficient level of operation. The present invention is particularly directed to the solution of this problem.

It is the primary object of this invention to provide a furnace combustion chamber having a novel system for furnishing secondary air to the flame in the combustion chamber. Another object of the invention is to provide a system for supplying secondary air to a flame produced with fluid fuel, so that air is available to support combustion in the quantity and at the positions required. Still another object is to provide means for introducing air into the periphery of an elongated flame and at spaced positions along the entire length of the flame, in a manner such that essentially the complete requirement for oxygen by the flame is satisfied. Still another object of the invention is to provide a novel and improved means for introducing secondary air into the combustion chamber of a boiler being fired by a liquid or gaseous fuel under pressure, so that fresh, warm air is supplied to the flame throughout the entire length of the combustion chamber. Other objects and advantages will become apparent from the following description of a selected embodiment of the invention and from the drawings, in which:

FIGURE 1 is a schematic, side elevational view of a steam boiler incorporating the invention, with parts having been broken away to more clearly illustrate structural details; and

in FIGURE 1.

The present invention has particular utility in connection with steam boilers and, therefore, is shown and described in connection with such apparatus. However, it will be understood that certain of the principles of this invention may be used to advantage in connection with other forms of heat-producing units.

In connection with steam boilers, whether of the water tube or fire tube type, there has long existed a need for achieving greater thermal efficiency for such units. Consequently, over the period of many years, considerable research and development work has been done in connection with steam generating units and many different designs and combinations have resulted. Substantial advances have been made in connection with improved fluid fuels, gas and oil, and the burners used in producing heat from such fuels. Furthermore, there has been quite a bit of development work in connection with providing im- 3,174,530 l atented Mar. 23, 1965 ciency of the known types of boilers is not very great when compared with their potential Furthermore, the incomplete combustion achieved with the known types of heating units results in substantial deposits of carbon and hydrocarbon particles, which serve to insulate the boiler tubes and thus prevent satisfactory heat exchange between the fire and the water being heated to produce steam. Then, too, there is considerable loss of organic particles through the flue or chimney, which has presented serious air pollution problems in heavily populated and industrial areas. The present invention greatly minimizes such problems by providing a more efiicient system for introducing oxygen, in the form of'air, into the combustion chamber in a manner which greatly increases the combustion of the fuel and, therefore, increases the operational eificiency of the furnace.

As seen in FIGURE 1, the invention is illustrated in connection with a water tube type of steam boiler 10, including a generally cylindrical boiler shell 12 and an underlying combustion chamber 14, which is substantially enclosed in refractory brick or the like. The boiler shell 12 includes a plurality of horizontal return water tubes 16. Each of the tubes 16 is in fluid-communication at its forward end with the header 18 into which water is introduced through a pipe 20, and the return portion 16a of each tube communicates with a steam discharge pipe 20a at the upper end of the boiler shell. The water enters the forward end of each tube 16 and is carried rearwardly of the boiler and then returned to a chamber 22 which is in communication with the steam discharge pipe 20a leading to a heating and/or power unit.

The combustion chamber 14 comprises a generally cylindrical metal vessel 24 which underlies the boiler shell and which is insulated therefrom by suitable insulating material 26. The rearward portion of the combustion chamber is open to permit the flow of heat upwardly into the boiler shell 12, where it passes between the tubes 16 to heat the water in the tubes, and the exhaust gases are discharged upward through a stack or chimney 28 at the forward end of the boiler. The cylindrical vessel 24 includes a forwardly extending portion 30 of reduced diameter, which projects outwardly beyond the forward Wall of the boil-er unit. The outer end wall 32 of projecting portion 30 of the combustion chamber has mounted therein a burner 34 of the type suitable for use with fluid fuel, such as gas or oil. A mixture of fuel and air particles is discharged from the burner under pressure and ignited to produce a flame extending generally axially of the combustion chamber. Since the structural details of the burner form no part of the present invention, a more detailed description of this apparatus is believed unnecessary.

In the illustrated embodiment, the forward extension 30 of the combustion chamber is also provided with a Waterwall, indicated at 36, which is generally an enclosed inner jacket surrounding the combustion chamber and through which water is circulated around the combustion chamber to provide for pre-heating of the water prior to its entry into the water tubes of the boiler. Suitable pumping means 38 is associated with the water supp-1y for providing forced circulation of the water from the bottom of the boiler and through the wat-erwall and then back into the boiler.

In addition to the primary air introduced into the burner along with the fuel to provide a combustible mixtune of air and fuel, there is provided a secondary air supply system which comprises generally a conduit 40 extending lengthwise of the combustion chamber and a series of annular tubes 42a-42e which are disposed in fluid-communication with the conduit 44) and positioned in generally coaxial, spaced-apart relation through out the length of the combustion chamber. More particularly, the secondary air system includes a variable delivery blower or fan '44 which is adapted to take air from the atmosphere and discharge it into the longitudinally extending conduit 4% in the combustion chamber. The air thus drawn in by the blower is preferably Warm and, in this respect, may be taken directly from the upper zone of the boiler room. It should also be noted that the conduit 40 enters the combustion chamber at a position adjacent the burner 34, so that the heat provided by the burner serves to also pre-heat the air being forced through the conduit.

The annular tubes 42 are each in fluid-communication with the air conduit 40, and these tubes are provided with a series of jet openings 48 which are disposed essentially around their entire circumference. T-he spacing of the tubes 42 and the spacing and size of the openi'ngs 48 are coordinated with the oxygen requirements of the burner flame, so as to thereby provide air in the quantity required to support complete combustion at positions spaced lengthwise of the flame. Furthermore, it may be desirable under certain circumstances to also provide a series of small openings or jets 46 in the contduit 40 on the upper side thereof facing the burner flame. It will be understood that the spacing and size of the openings 48, and the size and spacing of the openings 46, may vary with the type of burner and/or fuel being used. The rate of fuel supply and the mixture thereof with primary air will, of course, be factors in determining the type of flame and the oxygen requirements of such flame produced by the burner.

The openings 48 provided in the annular tubes 42 are directed inwardly of the combustion chamber, that is, in 'a direction generally toward the axis of the flame in the chamber. Preferably, the openings in the annular tube 42a at the forward end of the combustion chamber will also "be directed somewhat forwardly in the direction of the burner 34 and into the initial portion of the flame produced by the burner. The openings in the intermediate rings 42b, 42c and 42d are preferably directed approximately at right angles to the flame, that is, toward the axis of the flame, and the openings in the rear- .Wardly positioned annular tube 422 will preferably be directed somewhat forwardly, that is, toward the nozzle 50 of burner 34. In this way, the air jets will completely encircle the flame and generally follow the flame pattern, so as to most effectively provide the oxygen requirements throughout the length of the flame.

As indicated above, the particular arrangement of the described secondary air feed apparatus for any given furnace will be determined generally by the capacity and type of burner used, the size of the combustion chamber, and the type of fuel being burned. One way in which the most efiicient design for the secondary air feed system can be achieved is through analysis of the exhaust products, by means of the commonly used Orsat apparatus to determine the carbon dioxide (CO concentration, in conjunction with a pressure gauge on the blower fan 44. Maximum CO concentration is, of course, the objective in an external-combustion plant. Consequently, by varying the air feed from the blower 44, it can be determined what'pressure of air feed produces the greatest CO concentration as registered on the Orsat apparatus. Moreover, the spacing and disposition of the annular tubes 42 and the size, spacing and angle of the jet openings 48 therein can be similarly varied until the maximum CO concentration is registered by the Orsat apparatus. Once having experimentally determined the proper design for a given size combustion chamber and type of burner, the system can be duplicated for all similar combinations of burner and combustion chamber.

The principles of this invention have been used to advantage in one experimental installation with a boiler of the Scotch Marine type having a capacity of 20 B.H.P., wherein the combustion chamber is a 24 inch diameter iorrison tube having a length of 60 inches. A secondary air feed system comprising three annular rings, similar to rings 42 in the drawings, was installed in the combustion chamber, with each ring formed of one inch tubing and having an outside diameter of about 24 inches to conform closely with the inside diameter of the chamber. The first ring is spaced 10 inches from the burner nozzle and has one-fourth inch circular openings therein spaced one-fourth inch apart around the entire circumference of the ring, with the axis of these jet openings being disposed in facing relation to the burner nozzle and at about 45 degrees with respect to the longitudinal axis of the combustion chamber. The second ring is spaced two feet from the first ring and the jet openings therein are also one-fourth inch openings spaced at one-fourth inch intervals, but the jet openings are directed at right angles to the longitudinal axis of the combustion chamber. The third ring is essentially identical with the first ring, with the jet openings facing in the direction of the burner and disposed at about 45 degrees with respect to the longitudinal axis of the chamber. The burner is a guntype, using No. 1 fuel oil at a maximum rate of 7 gallons per hour. Air is fed into the annular rings at a rate of about 400 c.f.m.

The above described Scotch Marine boiler was tested prior to the installation of the secondary air feed system and was found to have a maximum CO concentration in the exhaust of 8%, with a stack temperature of 610 F. The secondary air feed system was then installed, with the same burner settings, and a sampling of the exhaust gases over an 8 hour period (30 samples) showed an average of 12.5% CO; concentration with a stack temperature of 500 F. Further, it was noted visually that the flame in the combustion chamber was brighter, more transparent and somewhat reduced in volume and disposed between the burner nozzle and the third ring in the secondary air feed.

Consequently, it is seen that with the described arrangement for the secondary air system in the combustionchamber, a substantial improvement results in the degree of combustion of the fuel. As a result, the hot gases which pass into the boiler shell from the combustion chamber contain a minimum of organic particles and, therefore, the amount of material deposited on the tubes, or on the boiler shell and other parts of the boiler, is greatly diminished. Since such deposits serve to insulate the boiler components and thereby reduce the heat transmission efficiency, there results a marked increase in the operational efliciency of the boiler unit.

Although shown and described with respect to a particular apparatus, it will be apparent that various modifications might be made without departing from the principles of this invention. Furthermore, it will be obvious that the disclosed secondary air system might be used to advantage in connection with other types of boiler units as well as other types of furnaces.

Various of the features of the invention believed to be new are set forth in the appended claims.

What is claimed is:

1. In a furnace having wall defining means providing an elongated combustion chamber including a burner at one end which is adapted to produce a flame by igniting a fluid fuel being discharged under pressure through a fuel discharge nozzle, means for introducing air into the combustion chamber at positions inwardly of the burner and in a direction generally toward the axis of the flame comprising an elongated main conduit extending within said chamber from a position adjacent the burner to a position adjacent the opposite end of the chamber, a plurality of generally annular tubular conduits disposed within the chamber in generally transverse relation to the longitudinal axis of the chamber and connected with said main conduit and spaced apart therealong at positions extending substantially the length of the chamber, each of said annular conduits including a series of jet openings which are directed only inwardly of the cornbustion chamber, and means for supplying a selected volume of air per minute under pressure through said main conduit to said annular conduits for ejecting air through said jet openings toward the axis of said chamber to thereby provide air around the entire periphery and essentially along the entire length of the flame produced by the burner, whereby the combustibles are confined within the flame and air is provided for the flame as needed along its length.

2. In a furnace having wall defining means providing an elongated combustion chamber including a burner at one end which is adapted to produce a flame by igniting a fluid fuel being discharged under pressure through a fuel discharge nozzle, means for introducing air into the combustion chamber at positions inwardly of the burner and in a direction generally toward the axis of the flame comprising an elongated main conduit extending Within said chamber from a position adjacent the burner to a position adjacent the opposite end of the chamber, a plurality of generally annular tubular conduits disposed within the chamber in generally transverse relation to the longitudinal axis of the chamber and connected with said main conduit at spaced apart positions extending substantially the length of the chamber, each of said annular conduits including a series of jet openings which are directed only inwardly of the combustion chamber, and a variable delivery blower means for supplying air under pressure to said main conduit and thence to said annular conduits for ejecting air through said jet openings toward the axis of said chamber, to thereby provide air around the entire periphery and essentially along the entire length of the flame produced by the burner, whereby the combustibles are confined within the flame and heated air is provided for the flame as needed along its length.

3. In a furnace having wall defining means providing an elongated combustion chamber including a burner at one end which is adapted to produce a flame by igniting a fluid fuel being discharged under pressure through a fuel discharge nozzle, means for introducing air into the combustion chamber at positions inwardly of the burner and in a direction generally toward the axis of the flame comprising an elongated main conduit extending within said chamber from a position adjacent the burner to a position adjacent the opposite end of the chamber, at least three generally annular tubular conduits, one of said conduits being disposed inwardly of and adjacent the end of said chamber remote from the burner, another of said conduits being disposed inwardly of and adjacent to said burner, and the remainder of said annular conduits being generally uniformly spaced intermediate said one and said another annular conduits, each of said annular conduits connected to said main conduit and extending in generally transverse relation to the longitudinal axis of the chamber and each including a series of jet openings which are directed only inwardly of the combustion chamber, and means for supplying a selected volume of air per minute under pressure through said main conduit to said annular conduits to eject air through said jet openings toward the axis of said. chamber, so as to provide air around the entire periphery and essentially along the entire length of the flame produced by the burner and thus confine the combustibles and flame within the pressure air in the chamber.

4. In a furnace having wall defining means providing an elongated combustion chamber including a burner at one end which is adapted to produce a flame by igniting a fluid fuel being discharged under pressure through a fuel discharge nozzle, means for introducing air into the combustion chamber at positions inwardly of the burner and in a direction generally toward the axis of the flame comprising an elongated main conduit extending within said chamber from a position adjacent the burner to a position adjacent the opposite end of the chamber, a plurality of generally annular tubular conduits disposed within the chamber in generally transverse relation to the longitudinal axis of the chamber and connected with said main conduit at spaced apart positions extending substantially the length of the chamber, each of said annular conduits including a series of jet openings which are directed only inwardly of the combustion chamber, said main conduit having jet openings therein intermediate said annular conduits and directed only toward the longitudinal axis of said combustion chamber, and a variable delivery blower means for supplying air under pressure to said main conduit and thence to said annular conduits for ejecting air through said jet openings toward the axis of said chamber, to thereby provide air around the entire periphery and essentially along the entire length of the flame produced by the burner, whereby the combustibles are confined within the flame and heated air is provided for the flame as needed along its length.

References Cited in the file of this patent UNITED STATES PATENTS 74,536 Horton Feb. 18, 1868 251,941 Probert et al. Jan. 3, 1882 539,021 Bartlett May 14, 1895 1,313,180 Grine Aug. 12, 1919 2,014,714 Bauer Sept. 17, 1935 2,072,731 Crosby Mar. 2, 1937 2,417,445 Pinkel Mar. 18, 1947 2,638,895 Swindin May 19, 1953 2,699,648 Berkey Jan. 18, 1955 2,958,194 Bayley Nov. 1, 1960 FOREIGN PATENTS 838,878 Great Britain June 22, 1960 

1. IN A FURNACE HAVING WALL DEFINING MEANS PROVIDING AN ELONGATED COMBUSTION CHAMBER INCLUDING A BURNER AT ONE END WHICH IS ADAPTED TO PRODUCE A FLAME BY IGNITING A FLUID FUEL BEING DISCHARGED UNDER PRESSURE THROUGH A FUEL DISCHARGE NOZZLE, MEANS FOR INTRODUCING AIR INTO THE COMBUSTION CHAMBER AT POSITIONS INWARDLY OF THE BURNER AND IN A DIRECTION GENERALLY TOWARD THE AXIS OF THE FLAME COMPRISING AN ELONGATED MAIN CONDUIT EXTENDING WITHIN SAID CHAMBER FROM A POSITION ADJACENT THE BURNER TO A POSITION ADJACENT THE OPPOSITE END OF THE CHAMBER, A PLURALITY OF GENERALLY ANNULAR TUBULAR CONDUITS DISPOSED WITHIN THE CHAMBER IN GENERALLY TRANSVERSE RELATION TO THE LONGITUDINALLY AXIS OF THE CHAMBER AND CONNECTED WITH SAID MAIN CONDUIT AND SPACED APART THEREALONG AT POSITION EXTENDING SUBSTANTIALLY THE LENGTH OF THE CHAMBER, EACH OF SAID ANNULAR CONDUITS INCLUDING A SERIES OF JET OPENINGS WHICH ARE DIRECTED ONLY INWARDLY OF THE COMBUSTION CHAMBER, AND MEANS FOR SUPPLYING A SELECTED VOLUME OF AIR PER MINUTE UNDER PRESSURE THROUGH SAID MAIN CONDUIT TO SAID ANNULAR CONDUITS FOR EJECTING AIR THROUGH SAID JET OPENINGS TOWARD THE AXIS OF SAID CHAMBER TO THEREBY PROVIDE AIR AROUND THE ENTIRE PERIPHERY AND ESSENTIALLY ALONG THE ENTIRE LENGTH OF THE FLAME PRODUCED BY THE BURNER, WHEREBY THE COMBUSTIBLES ARE CONFINED WITHIN THE FLAME AND AIR IS PROVIDED FOR THE FLAME AS NEEDED ALONG ITS LENGTH. 